Power tools driven by electrical motors are usually equipped with a reduction gear set. A switching device is also provided for selectively changing an output speed of the power tools. The switching device comprises a manual switch that is coupled to a cylindrical switching member axially movably received in a casing. The switching member has an inner gear serving as a ring gear of a planetary system coupled to and driven by the motor and an outer ring gear selectively engageable with an internal gear formed on an inside surface of the casing. The manual switch moves the switching member between an engaged position where the outer ring gear of the switching member engages with the internal gear of the casing and is thus prevented from rotation and a disengaged position where the outer ring gear of the switching member disengages from the internal gear of the casing and thus allows the switch member to rotate. This changes the output speed of other gearing system coupled to and driven by the planetary gear system associated with the switching member.
FIG. 5 shows an example of the conventional switching device of the power tool. Conventionally, the switching device comprises an arc member driven by the manual switch and slidably fit over an outside surface of the casing. The arc member has inwardly-extending projections extending through slots defined in the casing to drivingly engage with the switching member thereby forming a driving coupling between the manual switch and the switching member. Since extending the inwardly-extending projections through the slots to engage with the switching member is difficult and the structure is complicated, it is desired to have a simplified switching device that allows easy assembly thereof.